The present invention relates to a new and improved method of, and apparatus for, casting metal into a continuous casting mold, the metallic melt being cast from a ladle into an intermediate vessel or tundish having at least one-regulatable bottom discharge or outlet and then into at least one mold by means of a pouring tube, and further pertains to apparatus for the performance of the aforesaid method.
During continuous casting of metallic salts, especially steel, the melt is cast into a tundish from which it arrives at the mold of the continuous casting installation. The tundish possesses at least one discharge or pouring opening from which there flows out the metallic melt. Generally however there are provided a number of discharge openings, and one function of the tundish resides in uniformly distributing the melt to the discharge openings. The discharge openings, preferably in the case of large continuous casting installations, for instance for fabricating steel slabs, possess devices in order to regulate the throughflow of the metallic melt, for example by means of stopper rods or slide closures, by means of which the outflow cross-section is appropriately changed.
During the continuous casting of smaller cross-sections, for instance when casting steel in billet casting machines there are used in contrast outlets with defined cross-section which changes as little as possible during the entire casting time. The throughflow in this case is determined by the ferrostatic height in the tundish which is maintained within narrow limits and by the cross-section of the bottom discharge opening.
For casting with regulatable bottom discharges or openings at the tundish the state-of-the-art has advanced a number of proposals for using a ceramic pouring tube which normally immerses into the metallic melt. The enclosure of the casting jet with such type pouring tube affords a series of advantages. There is prevented the entry of oxygen to the casting jet and there is also avoided danger to the operating personnel by virtue of metallic spray. A more significant advantage for the continuous casting operation, however, resides in the fact that the casting jet penetrates from the tundish into the bath level of the mold without entraining the slag on the metallic melt, i.e. without mixing the slag into the metallic bath of the mold. The use of a pouring tube first permits with the aid of casting agents, preferably flux powder, to work in the mold in order to attain the known advantages.
The described casting with regulatable bottom discharges or outlets at the tundish and the subsequently arranged pouring tubes has been found in practice, notwithstanding the aforementioned advantages, to only be operationally reliable and economical for large continuous casting installations. The discharge devices require a relatively extensive maintenance and control in order to open free of disturbance at the start of the casting operation and to render possible the regulation operation. The useful times of the regulatable bottom discharge normally amounts to no more than 2 to 3 melts. Consequently there is the necessity of having a considerable number of tundishes. In the case of continuous casting installations with smaller strand cross-sections, for instance billet installations for steel, the aforementioned discharges with stopper rods and slide regulation or control cannot be used because of the previously given reasons.
At continuous casting machines for billets and blooms there are normally used at the present time non-regulatable bottom discharges. These discharges require, especially at the start of the casting operation, oftentimes a brief burning with an oxygen lance in order to permit the casting jet to begin to run in an operationally reliable manner and to regulate the desired casting jet formation.
There is further known to the art a method for casting steel into a continuous casting mold in which the steel is cast out of a ladle into a tundish having a non-regulatable bottom discharge through a pouring tube into the mold. For opening a non-regulatable closure body introduced into the tundish, upon reaching the desired bath level in the tundish an appropriately shaped infeed pipe for oxygen is introduced through the pouring tube located in casting position up to the bottom discharge or outlet and by infeeding oxygen the bottom outlet is opened. What is disadvantageous with this technique is, on the one hand, the cumbersome application of the oxygen infeed and, on the other hand, there is no possibility for influencing the formation of the casting jet at the start of casting. Furthermore with this technique after the start of casting it is not possible to undertake any corrections, such as for instance the burning-off of deposits in and at the discharge nozzle.